It is known that there is growing need to use high strength polymeric foams in lightweight applications a such as transport, in particular aerospace, mobile electronics, building materials, household goods, food service trays and medical, and the like. The use of said high strength polymeric foams, especially in light structures, such as for example in structural sandwich panels implies critical properties such as notably very high mechanical strength combined with excellent lightweight but also thermal resistance, flame resistance, environmental resistance, low-temperature impact resistance, thermal-insulating characteristics, soundproofing characteristics, vibration-proofing characteristics, chemical resistance, and recycling properties.
Polymeric foams made from a blend of polyarylene, in particular a rigid-rod polyphenylene with a poly(aryl ether sulfone) resin, in particular polyphenylsulfone has been described in WO 2006/094988 as an interesting polymeric foam having low density and high strength properties. It has been shown in WO 2006/094988 that blending small amounts of said rigid-rod polyphenylene polymers into a poly(aryl ether sulfone), in particular PPSU resin allowed the manufacturing of foams having a lower overall bulk foam densities while maintaining the mechanical properties of the rigid-rod polyphenylene polymer. Said foams were prepared by using a supercritical foaming process as described by Baldwin, D., in Polymer Engineering and Science, Vol. 36, No. 11, pp. 1437-1445, 1996 which is known as a batch foaming process. However, the working examples only show foams made from a specific polyphenylene 1 (i.e. rigid-rod polyphenylene copolymer, commercially available as PrimoSpire® PR-120 Self-Reinforced Polyphenylene, formerly marketed as PARMAX® 1200)/PPSU blend wherein the concentration of polyphenylene 1 is maximal 25 wt. %, based on the total weight % of polyphenylene 1 and PPSU, and the lowest foam density was achieved only at the very low polyphenylene 1 concentration of 6 wt. %.
One of the main issues in blending polyarylene polymers with aromatic poly(arylethersulfone) polymers, is the limited miscibility between the two polymers. Especially, the rigid-rod polyphenylene copolymer/PPSU polymer blends are suffering from this limited miscibility.
It is generally known that immiscible blends exhibit difficulties in foaming processes as notably used in the polymer foams industry. For example, nucleating agents as generally used in foaming processes can have a tendency to aggregate in one of the two distinct phases thereby causing notably weakening to foam cell walls. Another disadvantage is for instance that the immiscibility of the blend prevents uniform solubility of the blowing agent in the blend.
Thus, there is still a high need for foam materials comprising PPSU blends enriched with polyarylene polymers which can overcome all these drawbacks, as mentioned above, and whereby said foam material are characterized by having superior mechanical properties such as high stiffness and strength properties at a low foam density, improved thermal performance capabilities, in particular more robust resistance to very high temperatures used in the manufacturing of structural foamed articles and having improved chemical resistance while retaining all excellent foam properties such as a well defined, fine and fairly homogeneous cell structure, and whereby the high-strength foam articles made there from have excellent heat resistance, flame resistance, and environmental resistance, mechanical strength, and low-temperature impact resistance, and possesses excellent lightweight, thermal-insulating characteristics, soundproofing characteristics, vibration-proofing characteristics, chemical resistance, and recycling properties.